1. Field of the Invention
The present invention relates to a spring structure having a contact-preventing and rigidity-reinforcing function for a bed mattress, and more particularly to such a spring structure having a contact-preventing and rigidity-reinforcing function for a bed mattress in which the structure of a connection end portion for connecting a body spring and an exposure wire spring to each other is improved such that the connection end portion is not in close contact with an uppermost winding and/or a lowermost winding of the body spring and such that when a load is exerted to an exposure wire spring a displacement is prevented from being generated in which the exposure wire spring is leaned to one side, and rigidity of the spring is reinforced so that the exposure wire spring ascends/descends vertically only, thereby easily preventing the lateral displacement and deformation of the spring, preventing a noise due to a frictional contact, and extending the lifespan of the spring.
2. Background of the Related Art
In general, a bed mattress is mounted on a bed frame and is used as means adapted to provide a cushion force and buffering force. The bed mattress basically includes a spring assembly, an intermediate member laminatedly attached on the upper and lower surfaces of the spring assembly, an edge former fittingly attached to the circumferential edge of the spring assembly, and a cover member for protecting the surfaces of the intermediate member and the edge former.
Especially, the spring assembly is composed of springs vertically arranged spaced apart from one another at regular intervals over the entire area of the bed mattress, and a helical coil for securely engaging the springs with one another.
Herein, in order to better understand the present invention, a process for manufacturing a bed mattress will be hereinafter described in brief with reference to FIG. 13.
Referring to FIG. 13, the process for manufacturing the bed mattress includes the following steps of: fabricating a spring assembly 2 including coil springs arranged along row and column directions over the entire area of the bed mattress in such a fashion as to be spaced apart from one another at regular intervals, the coil springs being securely fixed by means of a helical coil; fittingly attaching an edge former as a support means to the circumferential edge of the spring assembly, and then continuously laminating multi-layered cushion means including a felt and a non-woven fabric as an intermediate member 4 on the upper and lower surfaces of the spring assembly 2; and covering the upper and lower surfaces and the circumferential edge surface of the intermediate member 4 as well as the outer surface of the edge former 3 with a cover 5, and then hermetically sealing a seam portion of the cover 5 with a sealing means 6.
Therefore, when a user sleeps or takes a rest, a load exerted to the bed mattress is absorbed and buffered by means of a cushion force of the intermediate member and a buffering force of the spring so that he or she can feel convenience and comfort.
Now, a spring structure for a conventional bed mattress constituting the spring assembly will be described hereinafter with reference to FIGS. 10a and 10b. 
FIGS. 10a and 10b illustrate an example of a conventional spring structure.
Referring to FIGS. 10a and 10b, a conventional spring 600 includes a body spring 10 formed in a coil shape whose diameter is gradually increased as it goes toward the top and the bottom from the central portion thereof, an upper end spring 16 wound and extending horizontally at a terminating point of the uppermost winding 12 of the body spring 10, and a lower end spring 18 wound and extending horizontally at a terminating point of the lowermost winding 14 of the body spring 10.
In this case, a distal end of the upper end spring 16 is fixed in such a fashion as to be twisted at the terminating point of the uppermost winding 12 of the body spring 10, and a distal end of the lower end spring 18 is fixed in such a fashion as to be twisted at the terminating point of the lowermost winding 14 of the body spring 10.
However, when the bed mattress is manufactured by employing the conventional spring, there are the following demerits:
A large or small load applied to the bed mattress is finally buffered and absorbed by the spring.
In this manner, when different loads are irregularly concentrated on the spring, there is a risk that the deformation of the spring may be progressed rapidly. In addition, adjacent springs come into close contact with each other according to the deformation of the spring to thereby contribute to the generation of a noise.
In view of these problems, another type of spring which has a dual buffer structure to decentrally buffer the larger and smaller loads separately has been manufactured, and its shape is shown in FIGS. 11a to 11c. 
Referring to FIGS. 11a to 11c, a conventional spring 700 of another type, as shown in FIGS. 10a and 10b, includes a body spring 10 formed in a coil shape whose diameter is gradually increased as it goes toward the top and the bottom from the central portion thereof, an upper end spring 16 wound and extending horizontally at a terminating point of the uppermost winding 12 of the body spring 10, and a lower end spring 18 wound and extending horizontally at a terminating point of the lowermost winding 14 of the body spring 10. The spring 700 is characterized in that a separate exposure wire spring 20 is formed integrally with the upper end spring 16 in such a fashion as to be disposed above the upper end spring 16.
At this time, a distal end of the upper end spring 16 is connected integrally with the exposure wire spring 20, and a distal end of the lower end spring 18 is fixed in such a fashion as to be twisted at the terminating point of the uppermost winding 14 of the body spring 10.
The exposure wire spring 20 has a diameter smaller than that of the body spring 10 and is configured to be wound in a coil shape. The exposure wire spring 20 also has a resilient force causing compressible deformation thereof relatively easily as compared to the body spring 10.
Especially, since a portion 24 (hereinafter, referred to as “connection end portion”) extending from the distal end of the upper end spring 16 to the exposure wire spring 20 runs spirally toward a vertical central axis of the overall spring, the connection end portion 24 and the uppermost wiring 12 for the body spring 10 positioned just below the connection end portion intersect each other when viewed from the top.
Accordingly, in the case where a smaller load (just a load applied to the bed mattress when a user twists and turns in his or her bed mattress) is exerted to the bed mattress, the exposure wire spring 20 buffers/absorbs the load impact. On the other hand, in the case where a larger load (a load applied to the bed mattress when the user sits on the bed mattress) is exerted to the bed mattress, the body spring 10 buffers/absorbs the load impact.
As such, the body spring and the exposure wire spring decentrally perform a buffering function thereof separately depending on the magnitude of the load exerted to the bed mattress to thereby provide advantages of preventing the deformation of the spring and prolonging the lifespan of the spring.
But, the conventional spring 700 of another type with the exposure wire spring has the following demerits:
As shown in FIG. 12, when the exposure wire spring 20 is compressed along with the exertion of a load to the bed mattress, and simultaneously the connection end portion 24 for connecting the distal end of the upper end spring 16 and the exposure wire spring 20 to each other is applied with a compression load, the connection end portion 24 and the uppermost wiring 12 for the body spring 10 positioned just below the connection end portion intersect each other when viewed from the top as described above. Thus, the connection end portion 24 comes into close contact with the uppermost wiring 12 while descending, to thereby generate the noise due to the contact therebetween.
Moreover, in the case where a larger load is exerted to the bed mattress, the exposure wire spring 20 is compressed and simultaneously the body spring 10 is also compressed, so that the connection end portion 24 also descends upon the compression of the exposure wire spring 20. At this time, the connection end portion 24 comes into close contact with the uppermost winding 12 of the body spring 10 with a larger impact, to thereby generate a larger contact noise.
As such, the contact noise caused by the spring during the use of the bed mattress acts as a great stress to a user, which may become a critical disadvantage for bed mattress products.
In addition, if the connection end portion repeatedly comes into close with the uppermost winding of the body spring by friction, it will not be long before the spring itself is deformed.
Moreover, since the direction of a load exerted to the bed mattress is not oriented uniformly such as vertically or slantly, there may occur a problem in that the exposure wire spring having a relatively weak rigidity as compared to that of the body spring is easily displaced laterally.
In this manner, when the exposure wire spring 20 is displaced in one direction, there is a problem in that an area of the bed mattress is locally depressed and a uniform cushion sense is not provided over the entire area of the bed mattress.